"Illegal wildlife trade is the most urgent threat facing species like tigers, rhinos and elephants. These animals are being killed every day to feed an escalating demand for their body parts," DiCaprio wrote on his Facebook page.

In Thailand, elephants are revered as a sacred animal. But the country currently allows ivory harvested from captive Thai elephants to be legally sold in its shops and marketplaces. All ivory for sale in the Kingdom is required by law to be certified by the Thai Provincial Administration Department as having come from legal sources, but critics say the system is rife with corruption and often gamed, and that Thailand has become a global hotbed for the illegal sale of smuggled African elephant tusks.

According to WWF, the illegal poaching of African elephants reached record levels in 2012, largely because of growing demand for ivory bracelets and decorative trinkets in China.

"Much of the ivory trade goes through Thailand," DiCaprio wrote. "We can help save these beautiful animals. Join me and the World Wildlife Fund and tell Thailand to ban all sales of ivory."

During a WWF-organized press conference at the landmark Central World mall in downtown Bangkok on Thursday, local Thai TV, film and radio talent -- including, Varin Sachdev, Pip Ravit Terdwong, Nampung Natrarika Thampridanant, Note Watcharabul Leesuwan and Egg Busakorn Tantiphana -- all joined the stage to call on Thai citizens to sign the DiCaprio backed petition.

The organizers are hoping to collect one million signatures before presenting the petition to Prime Minister Yingluck at the Convention on International Trade in Endangered Species of Wild Fauna and Flora (Cites), which will be held in Bangkok on March 3.

More than 400,000 people from Thailand and across the world have signed the petition so far, according to WWF. Other Hollywood names known to have joined the initiative include: Emily VanCamp and Josh Bowman from ABC’s Revenge, Lost’s Ian Somerhalder, actor Ethan Suplee, and Alyssa Milano.

“Every voice counts in the fight to stop the slaughter and save an iconic species that we revere as sacred,” Janpai Ongsiriwittaya, a local campaign leader for WWF Thailand said at the Bangkok event.